Automatic voltage regulator



8 J. c. MAY 3 AUTOMATIC VOLTAGE REGULATOR Filed Dec. 28, 1964 Sheet 2 ofs 35b C P A 566 556 I INVENTOR.

C. May

Jose /7 Dec. 31, 1968 J. c. MAY 3,419,788

AUTOMATIC VOLTAGE REGULATOR Filed Dec. 28, 1964 Sheet' 3 'of s n/ 36 7fi'' I g 34%| 35 4' E6 ifal $8? 53 Pavia M72 4 {ma} 1. 3%! 3] Y 'H J+ H71 U 29 28 Cl RCUIT L F SYNC j A E1222:

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INVENTOR.

Joseph 6'. May

' flTTOR/VEYJ United States Patent 3,419,788 AUTOMATIC VOLTAGE REGULATORJoseph C. May, Cheshire, Conn., assignor to The Superior ElectricCompany, Bristol, Coun., a corporation of Connecticut Filed Dec. 28,1964, Ser. No. 421,561 7 Claims. (Cl. 3236) ABSTRACT OF THE DISCLOSUREAn automatic voltage regulator for producing a substantially constantA.C. output voltage by initially providing an intermediate voltage andalgebraically adding thereto an alternating voltage derived from a DC.source and consisting of a stepped approximation of a sine wave whosevalue, either in amplitude or phase, is varied as required to maintainthe desired value of output voltage.

The present invention relates to an alternating current automaticvoltage regulator for maintaining the value of an output voltagesubstantially constant with changes in the input voltage and the powercontrolled by the regulator.

While it has heretofore been proposed to provide regulators whichmaintain a substantially constant output voltage, in many respects theseregulators have not been found completely satisfactory. Many regulatorshave heretofore employed moving parts, such as slip rings, relays, etc.which inherently are objectionable by reason of mechanical wear oraction. In addition, other regulators have employed devices such asinductive impedances which are also inherently somewhat slow acting andtherefore decrease the time in which the output voltage may be correctedto its desired value with an abrupt change in the input voltage.

An object of the present invention is to provide an alternating currentregulator which is quite rapid in correcting the output voltage to itsdesired value when a change in the input voltage occurs.

Another object of the present invention is to provide an automaticvoltage regulator which provides an output of alternating voltage whichis relatively low in distortion and which is quite eflicient inoperation.

A further object of the present invention is to provide an automaticvoltage regulator which achieves the above objects but yet whichpresents a low internal impedance thereby enabling three phasealternating current to be regulated by a regulator for each phasethereof.

Still another object of the present invention is to provide an automaticvoltage regulator which may include semiconductor devices but yet thedevices are basically caused to function as on-oif switches rather thanas amplifying devices.

In carrying out the present invention the automatic voltage regulatorincludes a pair of input terminals connectible to a source ofalternating current and a pair of output terminals at which the outputvoltage that is maintained substantially constant appears. The inputvoltage is initially altered to an intermediate value of alternatingcurrent and in the specific embodiment shown is preferably substantiallythe minimum value which the output voltage rnay have with the maximuminput voltage. Added to the intermediate voltage is an alternatingcurrent which is derived from a source of direct current and is formedto approximate a sine wave similar to the sine Wave of the input andintermediate voltages in order to have an output voltage that issubstantially a sine wave. More specifically, the added voltage is astepped approximation of a sine wave having a plurality of levelspreferably at least three. Thus the output voltage consists of theinter- "ice mediate voltage with which is combined the alternatingcurrent stepped voltage to produce the desired value of output voltage.

In order to maintain the value of the output voltage at that desired,the regulator includes an error detector which produces a signal that isindicative of the deviation of the output voltage from a known valuewith the known value being either the value of the output voltagedesired or a different value of voltage bearing a relationship to thedesired value of output voltage. The signal controls the value of thevoltage of the stepped alternating current that is added to theintermediate voltage and in one embodiment of the invention the signalis employed to control the amplitude of the stepped alternating currentand by adding the intermediate voltage and the stepped alternatingcurrent in phase with each other, the value of the output voltage mayaccordingly be changed by the change in the amplitude of the lattervoltage. In another embodiment of the present invention the amplitude ofthe stepped alternating current is maintained constant but its phase isaltered with respect to the phase of the intermediate voltage andaccordingly the value of the output voltage is changed by changing therelationship of the phases between the two voltages.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is a block and schematic diagram of one embodiment of theautomatic voltage regulator of the present invention.

FIG. 2 is a view of voltage wave forms which exist in the regulator.

FIG. 3 is a schematic and block diagram of a further embodiment of thepresent invention.

FIG. 4 is a plurality of voltage wave forms which appear in theregulator of FIG. 3.

FIG. 5 is a further embodiment of the regulator of the presentinvention.

FIG. 6 is a view of various voltage wave forms which occur in theregulator of FIG. 5.

FIG. 7 is a vector diagram of the phase relationship of the voltages inthe regulator of FIG. 5.

Refenring to FIG. 1, the automatic voltage regulator disclose-d thereinis generally indicated by the reference numeral 10 and includes a pairof input terminals 11 and 12 that are connectible to a source ofalternating current, such as the usual volt, 60 cycle having a sine waveform. The input terminals are connected across the winding of anautotransfo rmer 13 having an intermediate tap 14. The output voltage ofthe regulator appears at output terminals 15 and 16 with the terminal 16being in effect connected to the input terminal 12 while the terminal 15is connected to the tap 14 through a lead that includes a primaryWinding 17 of a transformer 18.

It will be appreciated that with the structure set forth above thatthere is produced in the primary winding 17 an intermediate voltagewhich is less than the input voltage and as the former has a sine waveform, the latter also has a sine wave form and this wave form of theintermediate voltage is indicated in FIG. 2 by the reference numeral 19.The output voltage wave form excepting minor percentages of harmonicsand distortion, in FIG. 2, is indicated by the [reference numeral 20 andconsists of the intrerncdiate voltage 19 combined with an alternatingcurrent that has the shape shown by the wave form 21.

The wave form 21 is generally referred to as a stepped approximation ofa sine wave with each half cycle including end portions 22 which have avalue of .225 of the maximum value of the voltage of the wave form 21;an intermediate portion 23 which may have a value of .770; and a topportion 24 which may have a value of about unity. Preferably, as shown,the maximum amplitude of the stepped wave form 21 is about one-fourththe maxi- K mum value of the output voltage wave form 20 in order toenable the regulator to have a relative wide range of values of outputvoltage from which one is chosen to be maintained constant with changesin the input voltage values also over a relatively large range.

As shown in FIG. 2, the output voltage wave form 20 results from theaddition of the wave forms 19 and 21. The value of the output "voltagemay thus be changed by changing the amplitude of the wave form 21. Inthis embodiment "both the wave forms 19 and 21 are in phase with eachother. 'It is also noted that the portions 22 are each substantially 30,the portions 23 each substantially 30 and the portion 24 substantially60 of the 180 of each half cycle.

Referring to FIG. 1, the wave form 21, as the stepped alternatingcurrent, is made to appear in the secondary winding 25 of thetransformer 18 and is the output of a D.C. to AC. inverter 26. Theinverter 26 preferably may include a plurality of transistors or othersemiconductor devices which are switched on and off by a synchronouscircuit 27 that not only maintains the stepped alternating current fromthe inverter 26 in synchronism with the intermediate voltage 19 but alsoserves to maintain for each half cycle the duration of the portions 22,23 and 24. For controlling the amplitude of the stepped alternatingcurrent, the regulator includes a reference source 28 that is connectedto an error detector 29 with the latter being connected across theoutput terminals and 16. The error detector 29 produces a signal in alead 30 to an adjustable output direct current power supply 311. Asource of direct current is derived from the input terminals .by meansof a full wave bridge 32.

With the above structure, the reference source 28, which may beadjustable to change the value of the output voltage desired to bemaintained constant, produces an electrical value which is combined inthe error detector with an electrical value related to the actual valueof the output voltage to produce in the lead 30 a signal which isindicative of the difference between the output voltage 'value and thereference signal. The signal may be either a change in polarity or maybe a greater or lesser value of current or voltage. The adjustableoutput D.C. power supply 31 increases its output power when the signalindicates that the output voltage is too low to thereby increase theamplitude of the stepped alternating current wave form 21 or decreasethe amplitude thereof when the signal indicates that the value of theoutput voltage is greater than that desired.

It has been found that the use of a stepped alternating current onlyintroduces a small percentage of distortion in the output voltage andthe distortion is generally of the higher harmonics of the frequency ofthe sine wave. These higher harmonics may be effectively reduced by theuse of a filter 33 connected across the output terminals tuned to thefrqeuencies of the higher harmonics. It will thus be appreciated thatwith the present invention the percentage of the output current whichconsists of unwanted harmonics and is sometimes referred to asdistortion is relatively small in comparison with other type regulatorsand accordingly enables the present regulator to operate quiteefliciently.

In the regulator shown in FIG. 3 the same result is achieved as thatshown in FIG. 2 in thatthe output voltage consists of an intermediatevoltage which is combined with a stepped approximation of a sine wave.The regulator, as in the regulator shown in FIG. 1, includes manyidentical parts such as input terminals 11 and 12 connected to the samesource of alternating current and to an autotransformer 13 having a tap14 and output terminals 15 and 16. In addition there is the full waverectifying bridge 32 connected to the adjustable output D.C. powersupply 31, the reference source 28 and the error detector 29 togetherwith the filter 33. However, in place of the single transformer 18 thereis provided in the connection between the tap 14 and the output 15 five4 transformers denoted 34, 35, 36, 37 and 38 each of which has a primarywinding that is connected in series with the tap 14 and output terminal15 and a secondary winding that is connected to the output of squarewave inverters 34a-38a.

Referring to FIG. 4, the voltage that is added to the intermediatevoltage is the same as that shown in FIG. 2, Le. is a steppedapproximation of a sine wave, and its wave form is indicated in FIG. 4by the reference numeral 39. In order to achieve this wave form,however, the square wave inverter 34a produces the wave form 34b Whilethe other square wave inverters 3511-3812 produce the wave forms 35b-38brespectively. It will also be understood that with each wave form thereis a line 340- 380 which is the zero line for their respective waveform. Referring specifically to the wave form 3411, it is in phase withthe intermediate voltage wave form 40 (having a Zero line 40a) and hasan amplitude which may be considered as being 1.00. The wave form 35bhas an amplitude of 1.225 and is 30 advanced from the wave 34b. The waveform 36b has an amplitude of 0.500 and is 60 advanced while the waveform 37b has an amplitude of .500 and is advanced and finally the waveform 381) has an amplitude of 1.225 and is advanced from the zeroposition of the intermediate voltage wave form 40.

It will thus be appreciated that at any angle of each half cycle it thefive wave forms 3411-3811 are algebraically added together that theywill produce the stepped approximation of the sine wave form 39 which isa wave form identical to the wave form 21 in FIG. 2. Moreover, while therelative proportions of amplitude of each of the waves have been given,it will be appreciated that by varying the amplitude of all by the sameproportion that the amplitude of the wave form 39 may accordingly bevaried.

For providing the switching of the square wave inverters 34a38a intoconditions of positive and negative conduction to produce each of thehalf cycles of the wave forms 34b38b, the regulator in FIG. 3 includesan oscillator and logic circuit 41. The oscillator circuit producesoscillations at a frequency of 720 cycles per second which is twelvetimes the 60 cycle alternating current to which the input terminals 11and 12 may be connected in order to produce a pulse or other signal forevery 30 of the 60 cycle input alternating current and thus enablecontrol of the inverters at specific intervals after each zero crossingof the sine wave 40. Naturally it the frequency of the source is otherthan 60 cycles, then the oscillator may have a different frequency. Itwill be understood that the inverters 34a-38a preferably includesemiconductor devices which are either switched on or off and thus maybe more efliciently operated than if they were merely amplifyingdevices.

In the embodiment of the automatic voltage regulator of the presentinvention shown in FIG. 5, rather than having the amplitude of thestepped alternating current changed to provide the change in the valueof the output voltage, herein the stepped alternating current may have aconstant amplitude; however, its phase relation with the intermediatevoltage is changed. Thus when the two voltages are added they are addedvectorially thereby pro ducing an output voltage which may have itsvalue maintained at the desired value.

In the regulator in FIG. 5, there are again the input terminals 11 and12 connected to a source of 60 cycle alternating current together withthe autotransformer 13 having a tap 14. Additionally there are providedoutput terminals 15 and 16, filter 33, reference source 28 and errordetector 29. As in the embodiment shown in FIG. 3, the steppedalternating current is added to the intermediate alternating voltage bya plurality of transformers 34, 35, 36, 37 and 38 having their primariesconnected in series and their secondaries connected to square waveinverters 34a, 35a, 36a, 37a and 38a. Moreover, connected to each of thesquare wave inverters 34a38a is a source of direct current, indicated bythe reference numeral 42. In order to enable the different waves 34b-38bto be maintained in the same relationship with each other there isprovided the oscillator and logic circuit 41.

The initiation of each cycle of the circuit 41 to control the zerocrossing of the stepped alternating current wave whose wave form isshown in FIG. 6 and indicated by the reference number 43, is elfected byan adjustable phase shifting circuit 44 connected to the error detectortogether with a synchronous oscillating circuit 45 connected to have theinter-mediate voltage impressed thereacross. The circuit 45 introducesinto the phase shifting circuit 44, the timing when the intermediatevoltage (whose Wave form is shown in FIG. 6 and indicated by thereference number 46) begins each half cycle and the error detectorserves to shift, with respect to the signal from the oscillator 45,' thesignal to the circuit 41 to begin each half cycle. Thus the phaseshifting circuit 44 merely serves as a delay circuit with the value ofthe signal from the error detector 29 changing the amount of the delaywhich may be from zero up to 180 for each half cycle. The zero delayadds the stepped alternating current in phase with the intermediatevoltage while the 180 delay subtracts the stepped alternating currentfrom the inter-mediate voltage. Other phase delays between not only thetwo extremes mentioned but also for 180 to 360 result in changing thesum of the two voltages to produce the output voltage having the desiredvalue. The wave forms 43 and 46 in FIG. 6 are 60 apart or out of phaseand they are combined by the transformers 34-38 in the manner shownvectorially in FIG. 7. Thus the voltage of the wave form 46 is indicatedby the vector 46a while the voltage of the wave form 43 is indicated bythe vector 43a and the resultant output voltage is indicated by thevector 47. It will be thus understood that by changing the phaserelationship between the wave forms 43a and 46a, the value of the outputvoltage may thus be changed even though there will also be a changebetween the phase of the output voltage and the phase of the inputvoltage except for the two conditions when the stepped wave 43 isexactly in phase or exactly out of phase with the intermediate voltage46. Moreover, by controlling the phase relationship, i.e. between Zeroand 180 and 180 and 360, the output voltage may be made leading orlagging with respect to the phase of the input voltage.

It will accordingly be appreciated that there has been disclosed anautomatic voltage regulator which regulates an alternating voltageapplied to its input terminals to produce at its output terminals analternating current which is maintained at a substantially constantvalue. The regulation is achieved by producing an intermediatealternating voltage and then combining with it another voltage whichconsists of a stepped approximation of a sine wave. By varying theamplitude or the phase of the stepped alternating current by sensing theactual value of the output voltage, the output voltage may thus bemaintained at its desired value.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

I claim:

1. An automatic voltage regulator comprising input terminals connectibleto a source of alternating current, output terminals at which an outputvoltage having a substantially constant value appears, means connectedto the input terminals for producing an intermediate alternatingvoltage, a source of direct current, means connected to the directcurrent source for producing an alternating voltage having for each halfcycle a plurality of different voltage levels forming a stepped wavethat approximates a sine wave, means for combining the alternatingvoltage with the intermediate voltage to produce the output voltage,means for sensing the deviation of the output voltage from a known valueand producing a signal indicative of the deviation and means receivingthe signal and operative to control the value of the alternating voltageadded to the intermediate voltage, with the sum of the alternatingvoltage and intermediate voltage constituting the output voltage havingthe desired value.

2. The invention as defined in claim 1 in which the means forcontrolling the value includes means for adjusting the value of thedirect current to control the amplitude of the alternating voltage.

3. The invention as defined in claim 1 in which the means forcontrolling the value includes means for changing the phase relationshipbetween the alternating voltage and the intermediate voltage.

4. An automatic voltage regulator comprising input terminals connectibleto a source of alternating current, output terminals at which an outputvoltage having a substantially constant value appears, means connectedto the input terminals for producing an intermediate alter natingvoltage having a value related to the input voltage, a source of directcurrent, means connected to the direct current source for producing analternating voltage which is a stepped approximation of a sine wave andincluding a plurality of inverter means with each inverter meansproducing an alternating square wave with the phases of the square wavesbeing different from each other, means for combining the alternatingvoltage with the intermediate voltage to produce the output voltage,said means including a plurality of transformers with each having aprimary winding and a secondary winding, means connecting the primarywindings in series with each other, means connecting each secondarywinding to an inverter means, means for sensing the deviation of theoutput volage from a known value and producing a signal indicative ofthe deviation and means receiving the signal and operative to controlthe value of the alternating voltage added to the intermediate voltage,with the sum of the alternating voltage and intermediate voltageconstituting the output voltage having the desired value.

5. The invention as defined in claim 4 in which the relative voltagevalues of each of the square waves and the phase therebetween is suchthat when algebraically added together they produce the alternatingvoltage by a step approximation of a sine wave.

6. The invention as defined in claim 5 in which the means forcontrolling the value of the alternating voltage includes means forchanging the amplitude of each square wave while maintaining the samerelative voltage values therebetween.

7. The invention as defined in claim 5 in which the means forcontrolling the value of the alternating voltage includes means forshifting the phase of the alternating voltage with respect to theintermediate voltage while maintaining the same phase relationshipbetween each of the square waves.

References Cited UNITED STATES PATENTS 3,350,631 10/1967 Ingman 323-452,644,128 6/ 1953 Henrich 323-45 3,013,202 12/ 1961 Kusko 323--63,018,431 1/1962 Goldstein 323-45 3,171,968 3/1965 Sanborn 32345 ORIS L.RADER, Primary Examiner.

HAROLD HUBERFELD, Assistant Examiner.

U.S. Cl. X.R. 323-45

